The advent of electronic trip units allows the use of an electronic rating plug to set the circuit breaker ampere rating within a common-sized industrial-rated circuit breaker enclosure. Wherein earlier circuit breakers employing thermal-magnetic trip units were designed to meet the various circuit breaker ampere ratings by conforming the size of the circuit breaker components and the circuit breaker enclosure, a large variety of such circuit breakers were stored at the distribution site to meet the electrical distribution market requirements. U.S. Pat. No. 4,649,455 entitled "Rating Plug for Molded Case Circuit Breaker" describes one example of the use of an electronic rating plug to set the circuit breaker ampere rating.
U.S. Pat. No. 4,679,016 describes an industrial-rated circuit breaker design that is economically assembled in an automated process. The circuit breaker utilizes a thermal-magnetic trip unit to interrupt circuit current under overcurrent conditions within a protected circuit. To accommodate the various circuit breaker ampere rating requirements, the circuit breaker entails several sizes. It would be economically advantageous to use a common-sized enclosure with such a circuit breaker employing a thermal-magnetic trip unit in view of the lower cost with the thermal-magnetic trip unit per se.
Accordingly, one purpose of the invention is to provide a so-called "mechanical rating plug" to allow circuit breakers using thermal-magnetic trip units to be arranged within a common-sized enclosure in a manner similar to the circuit breakers using an electronic trip unit.